The present invention generally relates to the use of proppants in subterranean operations, and, more specifically, to treatment fluids comprising salt tolerant settling retardant proppants, and methods of using these treatment fluids in subterranean operations.
Subterranean wells (e.g., hydrocarbon fluid producing wells and water producing wells) are often stimulated by hydraulic fracturing treatments. In a typical hydraulic fracturing treatment, a treatment fluid is pumped into a wellbore in a subterranean formation at a rate and pressure above the fracture gradient of the particular subterranean formation so as to create or enhance at least one fracture therein. Particulate solids (e.g., graded sand, bauxite, ceramic, nut hulls, and the like), or “proppant particulates,” are typically suspended in the treatment fluid or a second treatment fluid and deposited into the fractures while maintaining pressure above the fracture gradient. The proppant particulates are generally deposited in the fracture in a concentration sufficient to form a tight pack of proppant particulates, or “proppant pack,” which serves to prevent the fracture from fully closing once the hydraulic pressure is removed. By keeping the fracture from fully closing, the interstitial spaces between individual proppant particulates in the proppant pack form conductive pathways through which produced fluids may flow.
In traditional hydraulic fracturing treatments, the specific gravity of the proppant particulates may be high in relation to the treatment fluids in which they are suspended for transport and deposit in a target interval (e.g., a fracture). Therefore, the proppant particulates may settle out of the treatment fluid and fail to reach the target interval. For example, where the proppant particulates are to be deposited into a fracture, the proppant particulates may settle out of the treatment fluid and accumulate only or substantially at the bottommost portion of the fracture, which may result in complete or partial occlusion of the portion of the fracture where no proppant particulates have collected (e.g., at the top of the fracture). As such, fracture conductivity and production over the life of a subterranean well may be substantially impaired if proppant particulates settle out of the treatment fluid before reaching their target interval within a subterranean formation.
One way to compensate for proppant particulate settling is to introduce the proppant particulates into the fracture in a viscous gelled fluid. Gelled fluids typically require high concentrations of gelling agents and/or crosslinker, particularly when transporting high concentrations of proppant particulates in order to maintain them in suspension. As many gelling and crosslinking agents are used in a variety of fluids within and outside of the oil and gas industry, their demand is increasing while their supply is decreasing. Therefore, the cost of gelling and crosslinking agents is increasing, and consequently, the cost of hydraulic fracturing treatments requiring them is also increasing. Additionally, the use of gelling and crosslinking agents may result in premature viscosity increases that may cause pumpability issues or problems with subterranean operations equipment.
Proppants coated with a water-swellable polymer have also been used to combat settling by reducing the effective density of the proppant; however, the polymers used in existing technologies are sensitive to the presence of salts, which causes proppant suspension to decrease significantly in water with high total dissolved solids (TDS). See, for example, Self-Suspending Proppant, R. P. Mahoney et al., SPE 163818, 2013. Treatment fluids with moderate to high ionic strength, e.g., brines and clay stabilizers, are commonly used in treatment fluids. The degree of success of a hydraulic fracturing operation depends, at least in part, upon fracture conductivity after the fracturing operation has ceased and production commenced, creating the need for products and methods that hinder the settling of proppant particulates in a treatment fluid.